U.S. Pat. No. 4,697,995 discloses an electric-motor gerotor-type fuel pump that comprises a pair of coaxially spaced end caps and a case that joins the end caps to form a closed pump housing. One of the end caps contains a fluid inlet for admitting fuel from a surrounding tank, and the opposing end cap contains an outlet for delivering fuel under pressure to an engine. An electric motor is disposed within the housing, and includes an armature rotatably journalled between the end caps and a stator that surrounds the armature. Electrical power is supplied to the armature through commutator brushes in the outlet end cap. A pair of intermeshing inner and outer gear rotors are positioned within the housing adjacent to the inlet end cap, and cooperate with inlet and outlet ports in the end cap for pumping fuel from the fuel inlet through the housing to the outlet, such that fuel within the housing is at substantially outlet pressure.
Although the gerotor-type fuel pump disclosed in the noted patent, assigned to the assignee hereof, has enjoyed substantial commercial acceptance and success, improvements remain desirable. One problem with the fuel pump disclosed in the noted patent lies in difficulty in aligning the inlet end cap and gerotor components during assembly of the pump. The outer gear rotor is surrounded in assembly by a cam ring having an annular bearing surface for sliding engagement with the outer gear rotor. The cam ring is affixed by screws to the opposing surface of the end cap. Slotted holes in the cam ring accommodate adjustment during assembly. However, even with assembly tooling, it remains difficult to mount the cam ring to the end cap so that the cam ring bearing surface is coaxial with the outer gear rotor. Furthermore, requirement for provision of outlet fuel passages and the like in the cam ring add to cost and complexity of manufacture.
Another problem with existing fuel pump constructions lies in generation of pressure pulsations during operation of the pumping mechanism. These pressure pulsations not only cause audible noise that is annoying to occupants of the associated vehicle, but also make attempts at automatic fuel control more difficult to implement. A number of attempts have been made to reduce pressure pulsations in the pump outlet fuel line, such as by tailoring design of the pump outlet check valve.
It is therefore a general object of the present invention to provide a gerotor-type pump that finds particular utility in automotive fuel delivery systems and like applications, that is less expensive to manufacture and assembly than are pumps of similar type heretofore proposed, and that obtains reduced pressure pulsations in the pump output as compared with prior-art pumps of a similar character without deleteriously affecting pump delivery.